The present invention relates to golf balls and, more particularly, to improved golf balls comprising multi-layer covers which have a comparatively hard outer layer and a relatively soft inner layer, and a unique dual core configuration. The golf balls of the present invention exhibit relatively high PGA compression values. The present invention golf balls utilize one or more cover layers formed from a polyurethane material. Preferably, such polyurethane cover layers are formed from a reaction injection molding (xe2x80x9cRIMxe2x80x9d) process. The improved multi-layer golf balls provide for enhanced distance and durability properties over single layer cover golf balls.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E. I. DuPont de Nemours and Company under the trademark Surlyn(copyright) and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks Escor(copyright) and Iotek(copyright), have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (transpolyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play.
lonomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. durability, etc., for golf ball cover construction over balata. However, some of the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because although the ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction, and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since the ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionomeric resins lack the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers.
As a result, while there are currently more than fifty (50) commercial grades of ionomers available both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e., relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e., xe2x80x9cspin,xe2x80x9d xe2x80x9cfeel,xe2x80x9d etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Consequently, a number of two-piece (a solid resilient center or core with a molded cover) and three-piece (a liquid or solid center, elastomeric winding about the center, and a molded cover) golf balls have been produced to address these needs. The different types of materials utilized to formulate the cores, covers, etc. of these balls dramatically alter the balls"" overall characteristics. In addition, multi-layered covers containing one or more ionomer resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired.
This was addressed by Spalding Sports Worldwide, Inc., the assignee of the present invention, in U.S. Pat. No. 4,431,193 where a multi-layered golf ball is produced by initially molding a first cover layer on a spherical core and then adding a second layer. The first layer is comprised of a hard, high flexural modulus resinous material such as type 1605 Surlyn(copyright) (now designated Surlyn(copyright) 8940). Type 1605 Surlyn(copyright) (Surlyn(copyright) 8940) is a sodium ion based low acid (less than or equal to 15 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 51,000 psi. An outer layer of a comparatively soft, low flexural modulus resinous material such as type 1855 Surlyn(copyright) (now designated Surlyn(copyright) 9020) is molded over the inner cover layer. Type 1855 Surlyn(copyright) (Surlyn(copyright) 9020) is a zinc ion based low acid (10 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 14,000 psi.
The ""193 patent teaches that the hard, high flexural modulus resin which comprises the first layer provides for a gain in coefficient of restitution over the coefficient of restitution of the core. The increase in the coefficient of restitution provides a ball which serves to attain or approach the maximum initial velocity limit of 255 feet per second as provided by the United States Golf Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer layer provides for the advantageous xe2x80x9cfeelxe2x80x9d and playing characteristics of a balata covered golf ball.
In various attempts to produce a durable, high spin ionomer golf ball, the golfing industry has blended the hard ionomer resins with a number of softer ionomeric resins. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid, and an acrylate ester. It has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of hard ionomer alone. It would be useful to develop a golf ball having a combination of softness and durability which is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend.
Although satisfactory in many respects, currently known golf ball constructions and the combinations of materials used therein are in need of improvement. Specifically, a need exists for alternative golf ball designs and materials that enable a wide array of properties and playability characteristics to be achieved.
These and other objects and features of the invention will be apparent from the following summary and description of the invention, the drawings and from the claims.
The present invention provides all of the foregoing noted features and benefits, and in a first aspect, provides a golf ball comprising a center core component, a core layer disposed about the center core component, an inner cover layer disposed on the core layer, and an outer cover layer disposed on the inner cover layer. The inner cover layer has a Shore D hardness of less than 45. The outer cover layer in contrast, has a Shore D hardness of at least 50. Furthermore, the outer cover layer comprises a polyurethane material.
In yet another aspect, the present invention provides a golf ball comprising a center core component, a core layer disposed on the core center component, an inner cover layer disposed on the core layer, and an outer cover layer disposed on the inner cover layer. The inner cover layer has a thickness of from about 0.0075 inches to about 0.0225 inches. The outer cover layer similarly, has a thickness ranging from about 0.0075 inches to about 0.0225 inches. The outer cover layer comprises a polyurethane material.
In a further aspect, the present invention provides a golf ball comprising a core assembly and a multi-layer cover assembly disposed about the core assembly. The multi-layer cover assembly has a thickness of from 0.015 to 0.045 inches. The multi-layer cover assembly includes one or more cover layers that are formed from a polyurethane material.
In yet another aspect, the present invention provides a method for forming a golf ball comprising the following steps. A core center component is provided, about which is formed a core layer. An inner cover layer is formed on the core layer such that the inner cover layer has a thickness ranging from about 0.0075 inches to about 0.0225 inches. The method also involves molding an outer cover layer comprising a polyurethane material about the inner cover layer by use of a reaction injection molding technique.
In yet another aspect, the present invention provides a method of forming a golf ball having a dual core and a multi-layer cover assembly with a polyurethane cover layer via a reaction injection molding process. The method comprises the steps of providing a first material that is suitable for forming a core center component. Then a core center component is formed from that first material. A second material, different in composition than the first material, is then provided. The second material is suitable for forming a core layer. A core layer is then formed about the core center component from the second material. A dual core assembly is thereby produced. A third material is provided which is suitable for forming an inner cover layer. The method further involves the step of forming an inner cover layer about the dual core from that third material. A fourth material, different in composition than the third material, is provided. The fourth material is suitable for forming an outer cover layer. An outer cover layer is then formed on the inner cover layer from the fourth material. A multi-layer cover assembly is thereby formed. The method further involves selecting and providing the third and fourth materials such that at least one of those materials comprises a polyurethane material. Furthermore, the steps of forming the inner cover layer and the outer cover layer are performed such that the thickness of the multi-layer cover assembly is from about 0.015 inches to about 0.045 inches.